Many halogenated compounds are employed for a variety of practical uses, for example, as pesticides, soil fumigants, solvents, etc. It is known that a number of such compounds, particularly polyhalogenated compounds are toxic to plant and animal life. Although some of the compounds are bio and/or photodegradable (so they soon disappear from the environment) a substantial number are resistant to environmental degradation and remain in poisonous forms for many years. At present there are numerous processes available that will degrade such compounds into environmentally safe products.
Recent articles describing processes for the dehalogenation of organic materials, more specifically, for the destruction of polychlorinated biphenyls are Science News, Vol. 116, Nos. 25 and 26, page 422 (December 1979) and Electronic and Engineering Times, Oct. 29, 1979, pages 1 through 4.
U.S. Pat. No. 4,284,516 discloses and claims a process for the dehalogenation of low level concentrations (ppm-parts per million) of polychlorinated biphenyls (PCB's) dispersed within a contaminated substrate wherein said contaminated substrate is contacted with a reagent at a molar ratio of 25 to 500 moles of reagent per mole of halide contaminant contained within the fluid substrate; said reagent being prepared by:
(1) dispersing molten alkali metal selected from the group consisting of lithium, sodium and potassium at a temperature of at least 150.degree. C. in the contaminated substrate that is inert toward the alkali metal and has a boiling point above the melting point of the alkali metal in the ratio of 250 millimeters of contaminated substrate per mole of alkali metal; (2) cooling the dispersed molten alkali metal/contaminated inert fluid mixture to ambient temperature with vigorous agitation under an inert atmosphere; (3) adding 1.3 moles of an aromatic radical anion forming compound selected from the group consisting of biphenyls, alkyl substituted biphenyls, napthalene, alkyl substituted naphthalene, anthracene, alkyl substituted anthracene, naphthacene, alkyl substituted naphthacene, ortho, meta and para terphenyl, and alkyl substituted terphenyls dissolved in a nonhydroxylic ether containing solvent with stirring.
The process of U.S. Pat. No. 4,284,516 provides effective dehalogenation through treatment with an alkali metal aromatic radical anion reagent wherein the reagent is prepared by disbursing molten alkali metal in an inert fluid. The specifics of reagent preparation and molar treatment ratios are discussed in detail in the U.S. Pat. No. 4,284,516 patent. Said U.S. Pat. No. 4,284,516 is herein incorporated by reference and made a part hereof.
The examples and discussion of U.S. Pat. No. 4,284,516 teach the quenching of the excess reagent, specifically sodium naphthalide, with an excess of water. The water is removed and the solvent is dried by evaporation under vacuum. The process of the present invention is specifically directed to an improvement on the U.S. Pat. No. 4,284,516 patent in that the difficulties and disadvantages associated with a water quench of the alkali metal aromatic radical anion reagent are overcome by utilizing carbon dioxide (CO.sub.2) as the excess reagent quenching material.
The chemical reaction disclosed in U.S. Pat. No. 4,284,615 or for that matter any chemical reaction involving alkali metals has the potential to be hazardous even when conducted by qualified and experienced personnel. Extreme caution should be taken in this or any similar reaction involving organoalkali metal compounds, specifically organosodium compounds. Rapid generation of hydrogen is to be expected if sodium is contacted with water. For this reason utilization of U.S. Pat. No. 4,284,516 requires that adequate precautions be taken to assure that no metallic sodium enter the treatment vessel and that the water quench step be conducted in such a way as to avoid any possible explosive hazard.
The water quench, according to U.S. Pat. No. 4,284,516, should be added in small amounts, over a lengthy period of time, to control the rate of hydrogen release. Nitrogen or a similar inert gas should be used as a blanket to prevent the formation of potentially explosive hydrogen/oxygen mixtures.
U.S. Pat. No. 4,326,090 is very similar to U.S. Pat. No. 4,284,516, except that U.S. Pat. No. 4,326,090 teaches and claims the use of sodium naphthalide in the presence of sodium metal. The U.S. Pat. No. 4,326,090 disclosure does not suggest how the excess reagent is neutralized, but only says the process can be continuous with makeup quantities of naphthalene, solvent and sodium being added. It is evident that the process described in U.S. Pat. No. 4,326,090 or any dehalogenation process using alkali metals, would benefit from the improvement described in the instant invention.
As evidenced by the numerous corporations utilizing the process of U.S. Pat. No. 4,284,516 and the processes success in destroying highly stable PCB's, any improvement that would not generate an aqueous waste stream is desirable. Also, any improvement in the area of material recovery would also be desirable. The process of this invention allows for a nondistillative way for partial removal of the naphthalene from the bulk oil phase before or during processing. The prior art does not suggest or disclose the benefits that are attained through the use of the present invention.